In an instrument for measuring roundness, a surface roughness/shape measuring instrument, etc., the surface position of a work is detected by providing a contact at one end of an arm supported rotatably, biasing the arm so that the contact comes into contact with the surface of the work, and detecting the displacement of the other end of the arm. It is widely known that the displacement of the other end of the arm is detected by using a differential transformer system, in which a cylindrical iron core (core) is provided at the other end of the arm and two transformers are arranged continuously so that the core moves through the inside thereof accompanying the rotation, and is utilized when an alternating current signal is applied to one transformer, the alternating current signal induced at the other transformer changes depending on the position of the core, or a grating interference system in which movement accompanying the rotation of an optical grating provided at the other end of the arm is detected by an interferometer, etc. The present invention can be applied to any system as long as the system is provided with a contact at one end of an arm supported rotatably and detects the displacement of the other end. In the following explanation, a case is explained as an example, where the differential transformer system is used, however, the present invention is not limited to this.
FIG. 1A is a diagram showing a basic configuration of a displacement detector using a conventional differential transformer system. As shown in FIG. 1A, the displacement detector using the conventional differential transformer system has an arm 11 supported rotatably at the fulcrum of rotation 13, a contact 12 provided at a portion extending from one end of the arm 11, a spring that biases the arm 11 so that the contact 12 rotates toward the left side, a core 15 provided so that it moves on an arc with the fulcrum of rotation as its center from the other end of the arm 11 in accordance with the rotation of the arm, a cylindrical bobbin 16 provided so that the core 15 moves through the inside thereof, and a detection section 17 that applies a signal to the bobbin 16 and detects a signal that changes depending of the position of the core 15. Reference number 18 denotes a case in which the displacement detector and the fulcrum of rotation 13 is provided on the case 18, and spring 14 and bobbin 16 are fixed to the case 18. The detection section 17 is also provided on the case 18. In the following drawings, the case is not shown schematically for the purpose of simplification.
The bobbin 16 has at least two coils. When the detection section 17 applies an alternating current signal to at least one coil, the intensity of the alternating current signal induced at the rest of the coils changes monotonically depending on the position of the iron core (core) 15, and therefore, the detection section 17 detects the position of the core 15 in the bobbin 16 by detecting the intensity of the induced alternating current signal. The displacement detector using the differential transformer system is described in patent document 1, patent document 2, etc., and therefore, more explanation is omitted.
FIG. 1B is a diagram showing how the surface roughness etc. of surface A on the right side of a work W is measured using the displacement detector in FIG. 1A. As shown schematically, the displacement detector is moved to the right side of the work W and arranged so that the contact 12 comes into contact with the surface A on the right side of the work W. In this state, the arm 11 is biased by the spring 14 so that the contact 12 moves toward the left side and the contact 12 comes into contact with the surface A on the right side of the work W with a measurement pressure regulated by the spring 14. Then, when the work W or the displacement detector is moved in the vertical direction, the contact 12 is displaced in accordance with the surface shape of the surface A on the right side of the work W and the core 15 is displaced accordingly, and therefore, its displacement is detected.
The detection range in which the position of the core 15 in the bobbin 16 can be detected is a range in which the core 15 is in a predetermined positional relationship with respect to the bobbin 16. Consequently, in order to maximize the area of the surface of the work W in which the position can be detected, a setting is provided so that the average position of the work W on the surface corresponds to the middle in the predetermined positional relationship range. For example, when it is predicted that the surface A on the right side of the work W with which the contact 12 is in contact is the average position of the surface in FIG. 1B, the core 15 is arranged so that it is situated in the middle of the predetermined positional relationship range with respect to the bobbin 16.
FIG. 1C is a diagram explaining a case where surface B on the left side of the work W is measured using the displacement detector in FIG. 1A. The displacement detector in FIG. 1A has only one direction in which detection is possible, that is, the direction in which the left side of the contact 12 comes into contact with the work, and therefore, when the surface B on the left side of the work W is measured, the orientation of the entire displacement detector is changed by 180 degrees to reverse the direction of measurement and then the contact 12 is made to come into contact with the surface B on the left side of the work W. Such an operation is not only necessary in the case where the left and right surfaces of the work are measured, but also in the case where the surface and undersurface, the top and bottom surfaces, and the inner and outer diameters are measured.
When a measurement is made using the displacement detector as shown in FIG. 1A in a roundness measuring instrument, a surface roughness/shape measuring instrument, etc., in order to adjust the contact position between the contact 12 and the surface of the work, generally a work moving base that holds and moves the work, or a moving mechanism that holds and moves the displacement detector, that is, a moving mechanism that moves relative to the displacement detector with respect to the work is provided. Because of this, it is easy to move the displacement detector with respect to the work, however, it is complicated to rotate the displacement detector in order to measure a surface 180 degrees different as described above. For example, it is also possible to automatically change the measurement position by automatically controlling the movement by the moving mechanism, however, one more control system is required because a mechanism for rotating the displacement detector is provided. Under these circumstances, a displacement detector is needed, which is capable of measuring a surface 180 degrees in different directions without the need to rotate the displacement detector.
FIG. 2A is a diagram showing a basic configuration of a conventional displacement detector that meets such a need, and FIG. 2B and FIG. 2C are diagrams explaining the case where the left and right surfaces of the work W are measured.
As obvious from the comparison with FIG. 1A, the displacement detector in FIG. 2A differs from the basis configuration in FIG. 1A in that first and second contacts 12A and 12B extending in substantially 180 degrees in different directions are provided and at the same time, a rotation mechanism of the spring 14 that biases the arm 11 is provided so that the direction of biasing the arm 11 by the spring 14 can be changed by 180 degrees. Specifically, a member 19 that engages one end of the spring 14 is provided to the arm 11 and a mechanism that rotates a member 20 that engages the other end of the spring 14 is provided on the case.
As shown in FIG. 2B, when the surface A on the right side of the work W is measured, the rotation mechanism is set so that the spring 14 is situated on the right side of the arm 11 and the arm 11 is biased so that the contact 12A moves toward the left side, and then a measurement is made in the setting in which the contact 12A is in contact with the surface A on the right side of the work W.
As shown in FIG. 2C, when the surface B on the left side of the work W is measured, the rotation mechanism is set so that the spring 14 is situated on the left side of the arm 11 and the arm 11 is biased so that the contact 12B moves toward the right side, and then a measurement is made in the setting in which the contact 12B is in contact with the surface B on the left side of the work W.
The detection range is the same as that in the example in FIG. 1A.
Patent document 1: Japanese Unexamined Patent Publication (Kokai) No. H8-210804
Patent document 2: Japanese Unexamined Patent Publication (Kokai) No. 2005-10019